The emphasis of this proposal is to study tissue interactions, with emphasis on cartilage induction. The embryonic spinal cord and notochord stimulate somite chondrogenesis in vivo and in vitro. We have established that somite chondrogenesis can be stimulated in vitro by exogenous extracellular matrix components. Collagen (Types I, II, or III), proteoglycans (aggregates or monomers), or artificial matrices composed of proteoglycan-collagen complexes. The notochord (the in vivo inducer of somite chondrogenesis) has been reported to contain collagen Type II. Of the exogenous components used in vitro, collagen Type II or an artificial matrix containing collagen Type II, afforded the best chondrogenic differentiation. Chondrogenic differentiation is being assayed by Scanning and Transmission electronmicroscopy, and by determining the molecular profiles of proteoglycans and collagens synthesized before, during, and after differentiation. Proteoglycan analyses have shown that the somites respond differentially, depending upon the type of matrix component the tissues are exposed to during the culture period. Preliminary studies have shown that it is now feasible to analyze collagen synthesis before, during, and after chondrogenic differentiation.